The present invention relates to television systems, and more particularly to a digital signal processing (DSP) implementation for the video, audio, and data demodulators/receiver of a cable television (CATV) converter, satellite television receiver, multichannel multipoint distribution service (MMDS), or the like.
Cable television services are communicated from a headend via a cable distribution system to subscriber residences. At the subscriber residence, the drop cable which carries the signals from, e.g., a telephone pole, connects the-cable television signals either directly to the subscriber's television set or couples the signals through a converter and/or other subscriber electronics. A converter is necessary if the cable system supplies more than television channels 2 to 13. Only "cable-ready" television sets can tune the higher frequency cable channels above VHF broadcast channel 13. If additional channels, such as pay channels are supplied by the cable operator, they must be translated in frequency down to the frequencies employed by one or more channels to which conventional television sets can be tuned. For example, a cable television converter will typically output the selected cable television channel on the frequency used by broadcast channel 3 or 4, to which the subscriber television will be tuned as long as it is receiving signals from the converter.
Addressable converters are converters that can make channels available or unavailable in accordance with instructions sent in data packets from the cable headend. The converter includes a tuner controlled by the subscriber in order to pick out a specific channel. If a selected service is a premium service, it is scrambled and can be unscrambled only under control of data sent from the headend. Each subscriber has a unique electronic address, so that the cable headend is able to provide viewing authorizations to each addressable converter.
A typical cable television converter will include a frequency converter and filter (for allowing subscribers to tune to desired channels), a local oscillator, control circuits, a data receiver for authorizations, and a descrambler. It should be appreciated that receivers for satellite television and MMDS will contain comparable components. Where digital television signals are to be received in addition to analog signals, appropriate digital components must also be provided, generally including a downconverter for the transmitted digital signals, an analog-to-digital converter, a digital demodulator such as a QAM demodulator, a digital television decoder such as an MPEG decoder, onscreen display circuitry and a video encoder to provide the recovered television signals in an analog format for output to a conventional television.
Various television broadcast standards have been adopted in different parts of the world. These include the National Television Systems Committee (NTSC), phase alternating line (PAL) and SECAM standards. Each of the PAL and NTSC standards have different variations that are used in different parts of the world. For example, one NTSC standard is used in the United States. A somewhat different standard is used in Japan, and a variant thereof is used in Korea. Likewise, different variants of PAL have been adopted in different countries. A summary of the different NTSC and PAL television broadcast standards is set forth in Table 1.
TABLE 1 ______________________________________ Video Standard Audio Standard Sub-Carrier Comment ______________________________________ NTSC FM-Mono US NTSC BTSC Stereo SAP US NTSC FM/FM CUE Japan NTSC DIN (Variant) Channel ID Korea NTSC Mono-Privacy Proprietary NTSC Stereo-Privacy Proprietary NTSC Home-Theater (AC1) Proprietary PAL-B/G FM-Mono PAL-B/G NICAM DQPSK PAL-B/G DIN Channel ID Germany PAL-D FM-Mono China PAL-I FM-Mono PAL-I NICAM PAL-M FM-Mono Brazil PAL-N FM-Mono Argentina -- Music Choice DQPSK/AC1 ______________________________________
It would be advantageous to provide a cable television converter, satellite receiver, MMDS receiver, or the like that is able to process television signals regardless of the video standard used. However, in order to be economical, such converters must be able to be produced at low cost. This has been a difficult obstacle in the past, since different video standards required different circuitry including separate demodulators, filters, and associated components which rendered the cost of the final product prohibitive. Thus, multistandard television converters have not been made available.
It would be advantageous to provide a television converter that is capable of recovering video and audio signals according to different television standards. It would be further advantageous to implement such apparatus using digital signal processing techniques for both analog and digital television signal inputs. It would be still further advantageous to provide such a converter that is economical to produce using, e.g., a low cost very large scale integration (VLSI) application specific integrated circuit (ASIC) to provide the majority of the converter functions.
The present invention provides a converter having the aforementioned and other advantages.